A new government-sponsored agency called Financing Corp. yesterday sold $500 million worth of 30-year bonds in the first of a long series of steps to shore up the beleaguered fund that insures deposits at savings and loan associations.

Officials of the Federal Home Loan Bank Board, which regulates S&Ls and oversees the insurance fund, said investors snapped up the bonds at a yield of 10.73 percent -- about 0.9 percentage points higher than comparable U.S. Treasury security interest rates. About one-fourth of the issue was bought by Japanese investors, they said.

Financing Corp., or FICO, was created in August as part of an effort to pump money into the Federal Savings and Loan Insurance Corp. The FSLIC fund does not have enough money to pay for closing the nation's hundreds of insolvent savings associations.

The legislation that created FICO authorized it to issue up to $10.8 billion in bonds, but no more than $3.75 billion in any year. The Bank Board expects FICO to sell $400 million to $500 million worth of bonds every two or three months, officials said.

The FICO bonds are not guaranteed by the government, but financial market participants generally regard them as having an implicit guarantee.

No money was appropriated to bail out the FSLIC. Instead, 12 regional Home Loan Banks, which are private institutions owned by the S&Ls and savings banks in their regions, are to provide FICO with up to $3 billion in capital. Up to $2.2 billion of that money is to be used to buy long-term Treasury securities that pay no interest. These securities, which sell at a very deep discount and are redeemed for their full face value at maturity, will be held in custody of the New York Federal Reserve Bank to guarantee repayment of the new FICO bonds when they mature.

Interest on the new bonds will be paid from money received from S&Ls when FICO levies an annual assessment of up to nearly one-fifth of one percent of their deposits. An institution with $100 million in insured deposits could have to pay FICO more than $200,000 a year.

Most analysts expect the FSLIC fund eventually will need far more than $10.8 billion to close insolvent thrifts.

M. Danny Wall, chairman of the Bank Board, said the FICO money would allow FSLIC to finance some sales of troubled institutions to healthy S&Ls. He said the sales being contemplated will involve small to medium-sized S&Ls rather than any of the largest thrifts.